SUPERCONDUCTIVITY AND DENSITY WAVES IN HIGH DIMENSIONS

Density and pairing responses are studied for the Holstein molecular c rystal model. The charge density wave (CDW) and the superconductivity (SC) instabilities of the normal phase are investigated. Analytical re sults are obtained for small electron-phonon coupling in a simple cubi c lattice in the limit of large dimensionality (d = infinity). Near ha lf-filling the dominant instability is a CDW, due to nesting at q = (p i,pi,...). For larger deviations from half-filling the CDW becomes inc ommensurate in a narrow filling range and finally disappears. Then the SC instability dominates.